Just wondering about that (maybe this was already discussed than pls ignore):
Would it be possible and make sense to correlate the recommended hashrate to the actual transaction count in the que, so that it will enable to create blocks faster in times of high volume and makes it impossible to mine empty blocks?
It is impossible to know how many transactions are in everyone else's queue. You can only know how many transactions are in your queue.
If your queue doesn't exactly match every other queue in the world, then your difficulty won't match theirs and there will be no way for them to know if you chose a valid difficulty for your block.
